| 摘要 |
PURPOSE:To prevent howling by providing an analog/digital conversion circuit and a digital signal processor which removes a resonance frequency component from a digital signal. CONSTITUTION:A signal in which a sound fed back from a speaker 8 and a resonance frequency 13 are mixed is inputted to a microphone 9. In such a case, the signal including the resonance frequency 13 is converted into a digital signal by a second analog/digital conversion circuit 3, and the resonance frequency is detected by checking the character proper to the resonance by the resonance frequency detection circuit 11 of the digital signal processor 6, and frequency information is sent to a resonance frequency elimination circuit 12. The resonance frequency elimination circuit 12 eliminates a level of resonance frequency included in the digital signal. In such a way, a signal from which the resonance frequency is eliminated is converted into an analog signal (signal C) by a second digital/analog conversion circuit 5. The signal is converted into the one of two-wire system by a hybrid circuit 1, then, it is sent out to a line. |
